DNA sequence of woman who lived 115 years

London: Scientists have pieced together the entire DNA sequence of a woman who lived up to 115 years, a feat they say could give clues to why some people have such a long life.

The woman, whose identity is being kept secret and is known only as W115, is the oldest person in the world to have her genes mapped by Dutch scientists. The study, reported at a scientific conference in Canada, suggested the woman had genes that protected against dementia. She appeared to have some rare genetic changes in her DNA, said Dr Henne Holstege of the Department of Clinical Genetics at the VU University Medical Centre in Amsterdam.

It`s not yet clear what role they carry out, but it appears there is something in her genes that protects against dementia and other diseases of later life, Dr Holstege said. "We know that she`s special, we know that her brain had absolutely no signs of Alzheimer`s. There must be something in her body that is protective against dementia," Dr Holstege was quoted as saying by the BBC. "We think that there are genes that may ensure a long life and be protective against Alzheimer`s."

It is more than 10 years since the first draft of the human genetic code was revealed. Since then, perhaps a few hundred individuals have had their genes mapped in full, as the technology to "read" DNA gets better and cheaper. According to the researchers, W115 was born prematurely and was not expected to survive. But she lived a long and healthy life, and entered a care home at the age of 105.She eventually died from a stomach tumour, having been treated for breast cancer at the age of 100.She donated her body to medical science, allowing doctors to study her brain and other organs, as well as her entire genetic code.

A test of her mental skills at the age of 113 showed she had the performance of a woman aged 60-75 years.At post-mortem examination, doctors found no evidence of dementia or the furring of the arteries seen in heart disease.The work, which has yet to be published, was presented at the American Society of Human Genetics annual meeting in Montreal, Canada.

Commenting on the study, Dr Jeffrey Barrett, of the Sanger Centre in Cambridge, UK, said it was an important proof of principle. He said: "Sequencing the genome of the world`s oldest woman is an important starting point to understand how DNA variation relates to the process of having a long, healthy life. "But in order to really understand the underlying biology of living a long, healthy life, we will need to look at the DNA sequence of hundreds or thousands of people."